const lastname="Doe",age=30,job="carpenter";

var pi = 3.14;
var person = "John Doe";
var answer = "Yes I am !";

var carname = "Volvo";
document.getElementById("demo").innerHTML = carname;

// 变量的重新声明 值不变
var cername = "Volvo";
var cername;

// js的算术

x = 5;
x = y+2;

let variableName = value;

let city = '北京';
let age =30;
console.log(city,age);   //  输出 ：  北京 30

//  const 定义常量 ，赋值后值不变
const z = 10;
if(true){
    const z = 20;  // 不同的常量
    console.log(z);   // 输出20
}
console.log(z);   // 输出10


